Validity detector



.J. A. COOK, JR

May 17, 1966 VALIDITY DETECTOR 3 Sheets-Sheet 1 Original Filed April 27,1959 N 353 E Q g May 17, 1966 J. A. COOK, JR

VALIDITY DETECTOR 3 Sheets-Sheet 5 Original Filed April 27 1959 a w 6 MM3 w fi w wg Q S,

INVENTOR. 0 177 70 30 60 901/00 Jamesfloofifiz HIS gar 2 02M? SignalGeneracal' 5 fluzjvzu, Volts represents a permissible value of UnitedStates Parent 3,252,059 VALIDITY DETECTOR James A. Cook, Jr.,Wilkinshurg, Pa., assignor to Westing.

house Air Brake Company, Wilmerding, Pa., a corporation of PennsylvaniaOriginal application Apr. 27, 1959, Ser. No. 809,191, now Patent No.3,091,688, dated May 28, 1963. Divided and this application Nov. 2,1962, Ser. No. 235,042 8 Claims. (Cl. 317-149) My invention relates toinformation processing apparatus, and particularly to an improvedvalidity detector for evaluating the integrity of an information signal.

This application is a division of my copending application for LettersPatent of the United States, Serial No. 809,191, filed April 27, 1959,now Patent No. 3,091,688 for Validity Detector, and also assigned to theassignee of the present invention.

In many control and computing systems, input signals are supplied inaccordance with measurements continuously or intermittently made onvariables influencing the operation of the system. In general,'it isknown in advance that the magnitude, for example, of a given signal willbe within a prescribed range if the signal accurately the correspondingvariable. When such a signal departs from the prescribed range, theresulting operation of the system may be assumed to be erroneous orinvalid. Accordingly, it would I be desirable to preclude the admissionof such erroneous signals to the system. It is an object of myinvention, to provide a validity detector for evaluating a signal inaccordance with pre-determined criteria and applying the signalto asystem only if its characteristics meet the criteria.

As one specific example, in automatic classification yards for railwaycars it is desirable to measure the rolling resistance of each carentering the yard so that retarders in the yard may be set to properlycontrol the speed of the cars in their routes to selected classificationtrack-s. For example, one such automatic classification yard controlsystem is shown and described in the copending application of David P.Fitzsimmons and William A.-Robison, Jr., Serial No. 676,730, filedAugust 7, 1-957 and assigned to the assignee of my present application.

In such a system, it is possible to handle some cars using averagevalues of rolling resistance, rather than measured values, if enoughactual measured values are available for other cars. In general, theobserved rolling resistance of cars in a particular yard will fallwithin a predetermined range, for example, between 0 and pounds per ton.Accordingly, where apparatus is provided for measuring the rollingresistance of each car in such a yard, the measured value may beconsidered to be invalid if it is beyond the predetermined range. It isa particular object of my invention to provide means for detectingexcursions of a rolling resistance signal beyond such a predeterminedrange.

In some cars, such as partly loaded tank cars, fluctuation of the ladingmay cause the observed rolling resistance of the car to fluctuate in arandom manner. Obviously, a measurement of the rolling resistance at anygiven time of such a car would generally be meaningless. Accordingly, itis a further and more particular object of my invention to provide avalidity detector for checking the output stability of .a rollingresistance measuring system in an automatic classification yard.

It is a further object of my invention to provide a validity detectorfor checking that the measured value of a signal is within prescribedlimits.

It is a further object of my invention to provide a valid.

' tally one above the other with FIG. 1a at the top,

3,252,059 Patented May 17, 1966 ICC ity detector for checking that therate nal is within prescribed limits.

It is a further object of my invention to provide means for checkingthat the magnitude and the rate of change of a signal are withinprescribed limits and means for applying the signal to a signal storagedevice if the signal is within the prescribed limits.

In practicing my invention, in accordance with one specific embodimentthereof, a validity detector is connected to the output of a rollingresistance measuring system located on a stretch of measuring track in aclassification yard. In the validity detector, I provide means forsupplying the output of the rolling resistance measuring unit to astorage unit only if the measured value is below a predetermined limit.In this embodiment, the storage unit is of the type in which a signalmay be applied and followed for a period of time, and then stored by theoperation of a holding relay. The validity detector also includes afirst time delay unit for delaying the storage of the signal for apredetermined time after the rolling resistance measuring apparatus hasbeen energized, means for detecting whether the rolling resistance isabove a predetermined maximum value, and means for detecting whether themeasured value is below a predetermined minimum value. In order todetermine that the measured value is a stable equilibrium value, Iprovide means for measuring the rate of change of the rolling resistancesignal, and means for detecting excursions of this rate of change beyondpredetermined limits. I further provide a second time delay limit whichis actuated only after the predetermined time determined by the firsttime delay unit, and then only if both the magnitude of the measuredvalue and the rate of change of the measured value are within prescribedlimits. A switching unit is provided for actuating the storage relay ofthe signal storage unit. The switching unit is actuated by the. secondtime delay unit after its time delay if all the previous conditions forvalidity of the signal have been fulfilled.

The details of the above-described embodiment of my invention, as wellas other objects, features and advantages of my invention, will appearfrom a study of the accompanying drawings in connection with thedetailed description hereinafter given.

I shall first describe one embodiment of my invention in detail, andshall then point out the novel features thereof in claims.

In the drawings, FIGS. 1a and 1b, when placed horizoncomprise a wiringdiagram of one embodiment of my invention.

Referring now to the drawings, I have shown a stretch of trackcomprising rails 1a and 112 over which cuts of one or more cars areassumed to move in the direction shown by the arrow. This stretch oftrack is assumed to be located in a classification yard provided with anautomatic control system, which may, for example, be of the type shownand described indet-ail in the above-mentioned application Serial No.676,730. The stretch 'of track is divided, as shown, as by insulatedjoints 2, 3 and 4, into first and second track sections IT and 2T,respectively. As shown, track section 1T may form a part of aconvention-a1 track circuit comprising the rails of the section, a trackbattery TB1 and a normally energized track relay lTR. Track section 2Tmay form part of a conventional track circuit comprising the rails ofthe section, a track battery TB2 and a normal-1y energized track relay2TR. Accordingly, the occupancy of each of track sections IT and 2T willbe indicated by the release of the corresponding track relay in responseto the shunting of the track rails by the wheels and axles of a caroccupying the of change of a sigsection.

The apparatus just described, and certain contacts of the track relays,to be described, are shown in the drawings surrounded by a dotted lineand designated as a program unit 1. The function of this unit is toprogram, or time, a. measurement of rolling resistance of a cut of cars,in the manner described in the above-cited application Serial No.676,730, by marking the beginning and end of a measuring period.However, as will .appear, any other suitable program unit for timing ameasurement could be employed if so desired, without departing from thescope of my invention.

As described in the above-mentioned copending application Serial No.676,730, and shown, for example, in FIG. 7 thereof, and as moreparticularly described in detail in the copending application of Emil F.Brinker, Serial No. 727,388, filed April 9, 1958, now Patent No.3,089,029 for Measuring Apparatus, and assigned to the assignee of mypresent application, the rolling resistance of cuts of one or more carsrolling in track section 1T may be measured by a signal generator 5comprising a radar' velocity meter 6, a differentiator 7, and a biasunit 8. Since this apparatus is described in detail in theabovementioned copending applications, it will not be fully describedhere. Briefly, however, the radar velocity meter 6 measures the speed ofa car in section 1T and provides a signal which is differentiated bydifferentiator 7 to provide a signal in accordance with the accelerationof the cut. This signal is offset in bias unit 8, from amaxirnum of 100volts, in accordance with the value of the signal and a calibrationfactor proportional to the grade of the measuring section, in a mannerfully described in detail in the above-mentioned copending applications.For present purposes, it is sufficient to note merely that the output ofthe bias unit is a DC. voltage signal following a straight-linefunctional relationship between a maximum value of 100 volts when themeasured rolling resistance is 0 .and a value of 0 volts when themeasured rolling resistance is 25 pounds per ton. It should also bepointed out that, in the broader aspects of my invention, the output ofany signal generator having a predetermined output characteristic couldbe checked in the manner to be described.

As described in detail in the above-noted copending ap plication SerialNo. 676,730, the rolling resistance measured by the radar accelerometermay be stored in an electronic storage unit of the type shown at 18 inFIG. 1a. Unit 1 8 will be seen to correspond to unit 1-2G R 1-ESU inFIG/45 of application Serial No. 676,730. The details of such a storageunit are fully described in my copending application Serial No. 634,000for Electronic Storage Device, filed January 14, 1957, now Patent No.2,914,750 and assigned to the assignee of my present application.Broadly, however, as shown, electronic storage unit 18 comprises a DC.amplifier 23 having an input between terminal a and ground and an outputbetween terminal 0 and grounded terminal d.

As described in copending application Serial No. 634,000, the inputsignal to be stored is applied to terminal a of storage unit 18, andthence through a resistor R48, the back point of contact b of relay H,capacitor C6, back contact 0 of relay H and through resistor R47 toground. In the condition shown, output terminal 0 of amplifier 23 isconnected over back contact a of relay H and through resistor R47 toground to provide a first feedback circuit to the amplifier. ResistorR47 is thus connected in shunt within the input and output circuits ofthe amplifier. Wit-h relay H deenergized, the applied signal causescurrent to flow through resistor R48, capacitor C6 and resistor R47 inseries. While the capacitor is charged, the input and output circuits ofamplifier 23 are connected together and shunted by resistor R47.Accordingly, a voltage will be developed at the output of the amplifierin accordance with the internal characteristics of the amplifier. Thisvoltage will appear across resistor R47. The polarity of this voltagemay be equal or opposite to that provided by the applied signal. If thevoltages are opposite in polarity, capacitor C6 will be charged to avoltage equal to the d'itference between the applied signal voltage andthe voltage developed by the amplifier across resistor R47. If thevoltages are of the same polarity, the capacitor will be charged tovoltage equal to the sum of the applied signal and the voltage acrossresistor R47. In either event, the capacitor is charged to a voltagewhich differs from the voltage applied to terminal a of unit 18 by thevoltage developed across resistor R47.

The circuit constants are so chosen that capacitor C6 is chargedrapidly. When relay H is energized, the connection between the amplifieroutput circuit and the input circuit is interrupted at the open backpoint of contact a of relay H. The circuit for resistor R47 is nowopened at the open back point of contact c of relay H. The appliedsignal is now disconnected at the open back point of contact b of relayH. The closing of the front point of contact b of relay H now connects aresistor R46 in series with capacitor C6 in a feed-back path betweeninput terminal a and output terminal 0 of amplifier 23. A high value ischosen for resistor R46, and since the amplifier is arranged to havenegligible current flowing in the input circuit, capacitor 06 retainsits charge for a relatively long period of time, during which the storedvalue of the applied signal is available between terminal c and groundedterminal d of electronic storage unit 18. I

As described in copending application Serial No. 676,- 730, a series or"electronic storage units such as 18 may be provided, and switchingapparatus may be provided for connecting the rolling resistance signalto the first one of these units in the series that happens to beavailable, thus permitting the simultaneous storage of several values ofrolling resistance for different cars. Obviously, such provision couldbe made in the illustrated embodiment, but since this additionalapparatus forms no part of my present invention, it has not been shown.Further, it will be appreciated that the details of the storage unit donot form a part of my invention, and that any desired storage unit ofother utilization device could be employed if so desired.

The apparatus above briefly described is typical of that with which myinvention is adapted ,to be employed. The manner in which the voltagedetector of my invention is constructed and connected to cooperate withthe previously described apparatus will next be described.

As shown, in addition to the previously described apparatus, I haveprotvided a first form of time delay unit 9, a clamp v10, adiiferentiator' 15, first and second negative limit detectors .13 and16, first and second positive limit detectors 14 and 17, a second formof time delay unit 19, and a switching unit 20. The details of each ofthese units will first be described, and their connections to form avalidity detection system will then be described.

Delay unit 9 is adapted to provide a signal after a first predetermineddelay time, which may be to give one practical example, three seconds.This unit includes a capacitor C1, which is initially charged negativelyfrom a battery B 3 in program unit 1 over front contact b of track relay1TR. Thus, capacitor C1 is charged negatively as long as track "section1T is unoccupied. One end of capacitor C1 is grounded, as shown, and theother end is connected to the grid of a triode V1 having a groundedcathode. The grid of triode V1 is also connected, through a resistor R8,to the positive terminal of a suitable source of potential such as abattery B4. The plate of triode V1 is connected to the positive terminalof battery B4 through a suitable resistor R9. A diode D1 is connected tothe plate of triode V l as shown.

Normally, with track relay lTR in the condition shown, and capacitor C1negatively charged to the potential of battery B3, tube V1 will be cutoff and the plate of triode V1 will be at the potential of battery B4.

I may be 100 volts in the embodimentshown.

' Diode D1 will accordingly conduct as long as output terminal b of unit9 is below the potential of battery B4. When track section IT isoccupied, causing track relay ITR to release, the charging circuit forcapacitor C1 will be interrupted at the open front point of contact b ofrelay ITR, and capacitor C1 will discharge through resistor R8. In theembodiment shown, the value of 01 may be approximately .5 microfarad andthe value of resistor R8 may be 20 megohms. Battery B3 may have apotential of 100 volts, battery B4 may have a potential of300 volts andresistor R9 may be 100,000 ohms. Triode V1 may be one-half of a type6201 tube, and diode D1 may be a 1N540. With these components andconstants, after approximately three seconds capacitor C1 will havedischarged to an equilibrium value such that, taking into accounttheelfects of grid current which will prevent the grid from reaching thefull potential of battery B4, conduction of tube V1 will bring the platepotential to 150 volts. Accordingly, diode D1 will not conduct unlessoutput terminal b of the time delay unit is below 150 volts. The utilityof time delay unit 9 will be made apparent below.

Clamp 10 is inserted between the output of signal generator 5 and theinput of storage unit 18 to prevent the transmission of an outputvoltage below a predetermined value, which' may 'be 26 volts in theembodi-' ment shown, and which corresponds to a maximum transmittedvalue of rolling resistance of approximately 18.6 pounds per ton, itbeing presumed that any higher value would be spurious. As shown, clamp10 includes a triode V2, having its plate connected to the positiveterminal of a suitable source of potential, such as battery B5, and itscathode connected to ground through a resistor R7. A voltage dividercomprising a first resistor R6, the resistance element 12 of apotentiometer P1, and two resistors R5 and R4 are connected in seriesbetween the positive terminal of battery B5 and ground.

The wiper 11 of potentiometer P1 is connectedto the grid of triode V2,and is adjusted so that the voltage at the cathode of triode V2 is asuitable constant, which This cathode voltage is coupled through aresistor R2 to the junction of two resistors R1 and R3 as shown. Theother terminal of resistor'Rl is connected to output terminal aof-signal generator 5 over the back point of contact a of track relay1TR. The other terminal of resistor R3 is connected to input terminal aof electronic storage unit 18. A diode D2 is connected between thejunction of resistors R4 and R5 and the output terminal of resistor R3as shown.

In one embodiment of my invention, the value of resistor R6 is 100K,resistor 12 is 10K, resistor R5 is 27K and resistor R4 is 13K, Where Kstands for 1000 ohms. Accordingly, in this embodiment the voltage acrossresistor R4 is approximately 26 volts. Resistor R1 may be 200K, resistorR2 may be 800K, resistor R3 may be 330K and resistor R7 may be 47K. Thereason for the values of these constants will appear. The diode D2 maybe a 1N 540, battery B5 may be 300 volts, and triode V2 may comprise theother half of the type 6201 tube used for V1 in unit 9.

Referring now to FIG. 2, :it will be seen that the output of signalgenerator 5 is a negative-going positive voltage having a maximum valueof 100 volts, corresponding to pounds per ton of rolling resistance, anda minimum value of 0 volts, corresponding to a measured value of 25pounds per ton. Should other voltages appear in the output, they wouldbe assumed to be due to an invalid measurement or to faulty operation ofthe equipment. Moreover, it will be assumed that a voltage below about 6volts at the output of signal generator would representan.unrealistically low value of rolling resistance.

In the operation of automatic classification yards, it'

may be observed that better performance of the system is obtained if thevalues of rolling resistance measured in the measuring section arecorrected by a factor depending on the layout and operatingcharacteristics of the yard before applying them to predict theperformance of cars in the classification tracks. In the presentexample, it is assumed that the final value may be taken as a percentageof the measured value. In the embodiment shown, percent of the measuredvalue is transmitted to represent a typical correlation. In addition, itwill be assumed that any measured value of rolling resistance aboveabout 18.6 pounds per ton, corresponding to a signal generator outputvoltage of about 26 volts, is unrealistically high. In View of theseconsiderations, it is desired to modify the output of signal generator 5as shown in FIG. 3, such that the output of clamp 10 in response to asignal from signal generator 5 will never be less than 26 volts nor morethan volts, and above 26 volts will bear a linear relationship to thesignal generator output such that the clamp output will be approximately80 percent of the rolling resistance represented by the signal generatoroutput in this range. The manner in which the clamp functions to givethe characteristic shown in FIG. 3 will now be described.

Referring now to FIG. 1a, with the values given, the voltage acrossresistor R4 will be about 26 volts. Thus, due to the operation of diodeD2, if the potential at output terminal b of clamp 10 tends to fallbelow 26 volts, diode D2 will conduct to maintain it at 26 volts. Above26 volts, diode D2 acts as an open circuit. In this condition, thevoltage at output terminal b is determined by the ratio of resistancesR1 and R2 and the difference between the signal generator outputsupplied to terminal a of clamp 10 and the cathode potential of triodeV2, which is 100 volts in the example given. If resistor R1 is 200K andresistor R2 is 800K, as stated above, the voltage at output terminal bof clamp 10 will be the voltage at input terminal 'a plus 20 percent ofthe difference between 100 and the voltage at terminal a. It will beapparent that this relationship will lead to the output characteristiccurve shown in FIG. 3. As shown, the output is directly applied to inputterminal a of storage unit 18, but the storage 'will not be completeduntil relay H of storage unit 18 is energized in a manner which willsubsequently be described.

Referring now to FIG. 1b, negative limit detector 13 comprises a triodeV3, a diode D5, an input resistor R32, a plate resistor R33, and asuitable source of plate potential such as a battery B6. In theembodiment shown,

triode V3 may be half of a 6201'tube, D5 may be a 1N540, R32 may be a4.7 megohm resistor, R33 may be a 100K resistor, and battery B6 may beany suitable 300 volt source.

For voltages above approximately 6 volts applied through resistor R32 tothe grid of triode V3, conduction in triode V3 will lower the platepotential to volts or below. However, if the input voltage is below -6volts,

the triode will be cut off and the plate potential will rise to thepotential of battery B6, or to 300 volts in the embodiment shown. Thusdiode D5 will clamp output terminal b of negative limit detector 13 to aminimum of 150 volts for input voltages above, 6 volts, and will clampterminal b to a minimum of 300 volts for inputs to triode V3 below -6volts. The utility of this unit will become apparent hereinafter.

A second negative limit detector 16 in FIG. 1b may correspondstructurally to limit detector 13. However, for reasons that willappear, it is desired that limit de tector 16 function at -16 voltsinstead of .6 volts. For this purpose, the resistor in limit detector 16which corresponds to resistor R32 in detector 13 may be 1 megohm, andthe resistor that corresponds to resistor R33 may be 100K. Otherwise,the structure and operation of the two units are identical.

Positive limit detector 14 in FIG. 1b is somewhat similar in principleto the negative limit detectors described above, but includes a phaseinverter so that the output 7 clamp value is tra nstormed for excursionsabove a posi-' tive limit rather than below positivelirnit detector 14includes a first triode V8 having its plate, directly connected to thepositive terminal ofa suitable source of potential, here shown as abattery B7, Which-has its negative terminal grounded as shown. Thecathode of triode V8 is connected to ground through a cathode resistorR36 and a second source of potential such as a battery B8 having itspositive terminal cjonnected'to ground asshown The grid of triode V8 iscoupled to the negative terminal of battery B8 through a resistor R35.

a negative limit. As shown,

A second triode V9 in limit detector 14 has its grid the rollingresistance signal to values of less than +10 grounded, as shown, and itscathode directly connected to thecathode t tubeVfi so thatthe cathodecircuit comprising resistor R36Qand battery B 8 is common to bothtriodes. The plate of triode'viis'connected through a plate resistor R37to, the positive terminal of battery B7, and is connected through adiode D6 to output terminal bofdetector14..

In the embodiment shown, triodes V8 and V9 may both be enclosedin a type6201 envelope, diode D6 may be a 1N540, batteIiesBI and may each be300volts, resistor R35 may be 2 megohms, resistor R34 resistor R36 maybe 130K and resistor R37 may be 100K. With these values, triode V9 willnormally be conducting and the plate voltage will be 150 volts or belowfThe cathode voltage developed across resistor R36 will tend to limitconduction in triode V8. When a positive-going signal is applied toinput terminal a, a volt-age will appear at the grid of tube V8 tendingto increase. conduction in that triode; The increasedcurrent throughtriode V8 flowing through resistor R36 will raise the cathode p'o-t'en vtial of both triodes. When the signal applied between terminal a and,ground exceeds a predetermined value,. which will be .100 volts in theembodiment'shown, the current through triode V8 will be large enough toraise the cathmay be 750K,

through resistor R11.

would serve no useful purpose input signal applied between terminal aand'ground to the grid of triode V4. A voltage proportional-to the .rateof change will appear across resistors R10 and R13 in series, and willbe coupled to the grid of triode V4 Zener'diodes Z1 and-Z2 acrossresistor R10, as shown. 'As is known in-the art, these diodes have theproperty of blocking current flow in the'reverse"direction'for appliedvoltages up to a predetermined value, and'thereafter going to a lowimpedance state in which they act as conductors. The purpose of theseunits it to limit the measured rateof change'of volts and more than 10volts, since restriction to this range simplifies the'rema'iningcircuits, and because it to transmit greater variations.

Resistor R12 and capacitor C3 are included in a degenerative feed-backcircuit, to be described.

The second stage of 'differentiat'or comprises triode V5 and itsassociated circuits. T riodes V4 and V5 havea common cathode circuitcomprising resistor R14 and battery B9. The plate of triode VS'isconnected to the positive terminal of battery B10 through a plateresistor R15, Y

Grid bias for triode V5 is obtained from a potential divider extendingfrom the positive terminal of battery B10 through a resistor R16, theresistive element 22 of a potentiometer P2, and

ative terminal of battery B9. The wiper 21 of potentiometer P2 is'directly connected to the grid of triode V5 caused by signals applied tothe grid of triode cause a proportionate change in the current flowthrough triode V5 and a corresponding variation in the plate po- Inparticular,'it the signal on the ode potential sufficiently to cut offtriode V9 and the plate potential of triode Thus, output terminal b ofdetector14 is clamped to a minimumof .150 volts when the a is below 100volts, and to a minimum of 300 volts the input is above v100 volts,Should the voltage at out put terminal b tend to go below the clampedlevel in either I restore the voltage to the v case, diode D6 willconduct to clamped level. (Of course, there is nothing to prevent thevoltage atterminal ,b from being raised above the clamped. value ineither case.), The utility of unit 14 will V9 will then increase to S OOvolts.

' 'as shown.

Wiper 21 is so adjusted on potentiometer P2 that variations in thecathode voltage across resistor R14 V4 will tentialof triode V5; grid oftriode V4 increases in a positive direction, the current throughdiode V4Will increase and the cathode voltsignal applied to terminal 1 when ivolts. For this purpose, with the other components havi 1 ing the samevalues, the

resistors in positive limit detector 17 corresponding to res1storsR34R35, R36 andR37 may be 120K, 1J5. megohms, 120K and 100K, respectively.I,

Otherwise-the structure and operation are identical to those ofIirnitdet'ector 14. The utility of limit detector 17 will hereinafterappear. T i A I Diflerentiator 15 is provided in order to measure therate of change of the output of signal generator 5. This unit comprisestriodes V4, V5, V6 and V7, a pair of Zener diodes Z1 and Z2, apotentiometer P2, a suitable source of positive. potential such as abattery B10, a suitable source'of negative potential such as a batteryB9, and various resistors and capacitors, to be described.

The input stage of differentiator 15 comprises triode V4 and itsattendant circuitry. Triode V4 has its plate connected to the positiveterminal of battery B10, and its cathode connected to the negativeterminal of battery B9 through a suitable cathode resistor R14. Thebasic input circuit for the grid of triode V4 comprises capacitor C2,resistor R10 and resistor R13 in series. The function of capacitor C2 isto transmit only the rate of change of an grid of 'triodeV7, Variationsin cathode age Will increasecorrespondingly. This increased cathodevoltage applied to triode V5 will decrease the current flow throughplate resistor R15 and triode V5 and the voltage atthefplate of triodeV5 will increase.

The output appearing at th'eplate of triode V5 is resistance-coupled tothe grid of a third stage triode amplifier V6 by means of a seriespotential divider comprising resisto'rsR17 and R19. The plate of triodeV6 is connected to positive terminal of battery B10 through a suitableplate resistor R20 and the cathode is grounded as shown. Triode' V6accordingly operates-as conventional amplifier, with a negative goingsignal applied to the grid causing a rise in the voltage at the plate.

The last stageyof difierentiator 15 comprises triode V7 and itsassociated circuits. The plate of the previous stagetrio'de V6 iscoupled to the grid of triode V7 through a potential dividercomprisin'gresistor R21 and resistor R22, the latter being'connected throughbattery B9 to ground. The cathode of triodeV7 is coupled to the negativeterminal of'battery B9 by a sistor R23. The plate oftriode V7 isdirectly connected to the positive terminal .ofbattery B10, as shown.

A series potentialdivider extends from the positive terminal of batteryB10 through resistors R27, R24 and R23 in series to the negativeterminal of battery B9. As-

shown, a first output terminal b of the differentiator is connected tothe junction of resistors R24 and R27, and a second output terminal c isconnected to the junction of resistors R23 and R24. When a signal isapplied to the current cause fluctuations in the voltage across resistorR23 which are directly reflected at output terminals 12 and c.

The voltage at the cathode of triode V7 is fed back to. the input oftriode V4, high frequency components of the output being directlycoupled to the grid of-triode V4 through capacitor C3, and lowerfrequency components are connected back-to-back I a resistor R18 inseries to the negsuitable cathode redivider comprising resistors beingreturned to ground through resistors R12 and R13.

While a small portion of the lower frequency components are coupled tothe grid through resistors R10 and R11, the over-all function of thisfeed-back network is to attenuate high frequency components more thanlow frequency components, thus filtering out random noise in the inputsignal. Such noise is normally of a substantially higher frequency thanthe rate of change of the signal which is sought to be measured.

It will be observed from the above description that the stage comprisingtriode V4 is cathode coupled to the second stage in such a manner thatthere is no inversion between the signal at the grid of triodeV4 and theoutput at the plate of triode V5. Since triode V7 is a cathode follower,there is no inversion in that stage,.and since -there is a single phaseinversion in triode V6, the output of thediiferentiator is phaseinverted. Thus, the feedback just described is degenerative in nature.The over all operation of the differentiator will accordingly be seen toproduce signals at the output terminals b and proportional to the rate.of change of the signal applied to input terminal a, with highfrequency noise filtered out, and with variations in the input rate ofchange limited by the action of Zener diodes Z1 and Z2.

In the above-described dilferenti-ator of this embodiment, triodes V4and V5 may comprise a single 5751 tube, triodes V6 and V7 may comprise asingle 5814WA tube, and Z1 and Z2 may each be a voltage Zener diode.Batteries B9 and B10 may each be 300 volts. Capacitor C2 may be .25microfarad and capacitor C3 may be .004 microfarad. Resistor R10 may be10 megohms, resistor R11 may be 270K, resistor R12 may be 300K, resistorR13 may be 100K, resistors R14, R15, R16 and R18 may each be 220K,resistor R17 may be 2.2 megohms, potentiometer P2 may be 25K, resistorR19 may be 3.3 meg-' ohms, resistor R20 may be 100K, resistor R21 may be1.8 megohms, resistor R22 may be' 3.3 megohms, resistor R23 may be 68K,resistor R24 may be 120K, and resistor R27 may be 1 megohm.

Time delay unit 19 comprises a capacitor C4 having one end connected toground and the other end connected through resistors R38 and R39 inseries to the negative terminal of a battery B11, which has its positiveterminal grounded as shown. In the embodiment shown, capacitor C4 may be.15 mic-rofarad, resistor R38 may be 4.7 megohms, and resistor R39 maybe 10 megohms. With these constants, an input signal applied to inputterminal a of unit 19 will be transmitted to output terminal b with atime delay of approximately .7 second.

Switching unit 20 comprises a first triode V10, a second triode V11, adirect current relay VR, and associated circuits which will now bedescribed. Triode V10 has its cathode connected to ground as shown, andits plate connected to the positive terminal of a suitable source ofpotential, here shown as a battery B14, through a suitable plate reistorR40. The negative terminal of battery B14 is grounded. Normally, arelatively high voltage is applied to the grid of triode V10 ofswitching unit 20 in a manner to be described. A substantial currentwill accordingly flow through plate resistor R40, driving the plate to arelatively low potential. If the signal applied to input terminal abecomes sufliciently negative, triode V10 will be cut olf and its platepotential will rise to substantially the potential of battery B14.

The output of triode V10 is applied through a potential R41 and R42 tothe grid of triode V11. As shown, one terminal of resistor R41 isconnected to the plate of triode V10, the junction of resistors R41 andR42 is connected to the gridof-triode V11, and the other end of resistorR42 is connected to the negative terminal of a battery B13, which hasits positive terminal grounded, as shown. As will appear, when thepotential at the plate of triode V10 rises to substantiallythe potentialof battery B14, the potential at the grid of triode V11 will be highenough to cause substantial 10 current to flow in triode V11. 0n theother hand, in the normal state of conduction of triode V10, with theplate potential substantially below that of the positive terminal ofbattery B14, there will be a negative bias on the grid of triode V11which will cause it to be cut off.

The cathode of triode V11 is grounded. The plate is connected throughthe winding of relay VR and a resistor R43 in seriesto the positiveterminal of battery B14. Accordingly, when triode V11 is conducting,relay VR will be energized and will close its front contacts. At othertimes, relay VR will be deenergized and will close its back contact. Asshown, a capacitor C5 is provided which has one end grounded and theother end connected over the back point of contact b of relay VR to thejunction of a pair of resistors R44 and R45. These resistors arearranged in a potential divider circuit extending from ground throughresistors R44 and R45 to the negative terminal of battery B13, which hasits positive terminal grounded as shown. Accordingly, with relay VRreleased, capacitor C5 will be negatively charged to a value dependingon the potential of battery B13 and the ratio of resistors R44 and R45.With relay VR energized, capacitor C5 is disconnected from its chargingcircuit and is directly connected to the grid of triode V10 over thefront point of contact b of relayVR. This provides a slowly decayingvoltage at the grid of triode V10 which tends to maintain triode V10cutoff and triode V11 conducting to hold up relay VR for a fixed timeafter it has been energized, thus permitting the proper functioning ofthe external circuits controlled by relay VR.

The values of the components, in a practical embodiment of switchingunit 20 above described, are, for resistor R40, 220K; for-resistor R41,2.2 megohms; for resistor R42, 3.3 megohms; for resistor R43, 10K; forresistor R44, K; for resistor R45, 47K; and for capacitor C5, .1microfarad. Batteries B13 and B14 may each be 300 volts. Triodes V10 andV11 may be enclosed in a single 6201 envelope. Relay VR may -be a styleM miniature relay of the type manufactured by the Union Switch & SignalDivision of Westinghouse Air Brake Company.

Switching unit 20 includes a third source of potential comprising abattery B12, which has its negative terminal grounded, as shown, and itspositive terminal connectedto the heel of contact a of relay VR. Thefront point of contact a of relay VR is connected, as shown in FIGS. lband 1a, over the front point of contact a of track relay 2TR and thencethrough the winding of storage relay H in electronic storage unit 18 toground. Accordingly when relay VR is energized, if track section 2T isthen unoccupied, relay H will be energized to complete the storage ofinformation supplied to storage unit 18 as described above.

Time delay unit 9, negative limit detectors 13 and 16 and positive limitdetectors 14 and 17 each have their output terminals b connected toinput terminal a of time delay unit 19 as shown. As previouslydescribed, each of the terminals b of these units has a first conditionin which they are clamped to 300 volts and a second condition in whichthey are clamped to volts. Accordingly, capacitor C4 will be charged to300 volts if any of the other units is clamped to 300 volts, and will becharged to 150 volts if all of the other units 9, 13, 14, 16 and 17 areclamped to 150 volts. With capacitor C4 charged to 300 volts, atequilibrium, and with the constants given, a voltage of +18 volts(excluding the effects of grid current, which in practice would preventthe grid from going positive) will be applied to the grid of triode V10.When the last of units 9, 13, 14, .16 and 17 has been clamped to 150volts, and after the time delay of .7 second required for capacitor C4to discharge, the grid of triode V10 will be changed to approximately61.5 volts. At this time, triode V10 will be cut ofi, triode V11 willbecome conducting and relay VR will pick up.

Each of units 9, 13,-14, 16 and 17 checks a specific characteristic ofthe signal generator output, and is only clamped to 150 volts when thecharacteristic is within the prescribed range. Accordingly, relay VRwill pick up when and only when all of the prescribed characteristics ofthe signal have been checked.

The operation of this embodiment of my invention will 'now be described.First, it will be assumed that both track sections 1T and 2T areunoccupied and that track relays lTR and ZTR of program unit 1 areenergized as shown. With track relay lTR picked up, the output of signalgenerator is interrupted at the open back point of contact a of relay1TR.

With relay 1TR picked up, the negative terminal of battery B3 isconnected over the front point of contact of relay lTR to chargecapacitor C1 in time delay unit 9. Capacitor C1 will accordingly chargeto 100 volts, and triode V1 will be cut off. Withtriode V1 cut off, itsplate will be at a potential of 300 volts, and capacitor C4 in timedelay unit 19 will be charged through diode D1 in time delay unit 9until it is charged to 300 volts.

With the output of signal generator 5 interrupted, triode V3 in negativelimit detector 13 will conduct normally, and output terminal b ofdetector 13 will be clamped to l50 volts mini-mum. Each of the otherpositive and negative detectors will be similarly clamped, since theyare receiving no signal from the signal generator and accordingly arereceiving no signal outside of their set limits. However, since thevoltage across capacitor C4 is set to 300 volts by the action of timedelay unit '9, none of the positive or negative limit detectors willhave any effect on the circuit at this time.

With capacitor C4 charged to 300 volts, triode V will be conducting andtriode V11 will be cut ofi", causing relay VR to be released.

The absence of a signal at input terminal a of clamp 10 will cause thevoltage at output terminal b of clamp 10 to assume its minimum value of26 volts. This signal will be applied to input terminal a of storageunit 18, but the storage cannot be completed because the circuit forrelay H is interrupted at the open front point of contact a of relay VR.

Differentiator 15, with no input applied to its terminal a, will developfiXed potentials at its output terminals b and c which are Within therespective acceptable inputs for negative limit detector 16 and positivelimit detector 17.

Next, let it be assumed that a cut of cars moving in the direction shownby the arrow enters section IT and releases track relay lTR. The radarvelocity meter 6 will measure the speed of the cut and provide a signalwhich is differentiated in differentiator 7 and biased in bias unit 8 toprovide an output signal at terminal a of signal generator 5representing the rolling resistance of the cut. This signal will now beconnected to units of the validity detector apparatus over back contacta of track relay 1TR, in a manner to be described.

With track relay 1TR released, the charging circuit for capacitor C1 intime delay unit 9 will be interrupted and capacitor C1 will begin todischarge through resistor R8. However, for three seconds after theinterruption of the charging circuit for capacitor C1, sufiicient chargewill remain to keep the plate potential of triode V1 near 300 volts.Accordingly, capacitor C4 in time delay unit 19 cannot be dischargedbelow 300 volts for at least this three-second interval. This intervalis provided in order to insure an opportunity for the cut and themeasuring equipment to stabilize in performance, since the measuringsection is normally located on or near the hump in the classificationyard and it takes a short time after the release of each cut for the cutto settle down to normal rolling behavior. I

The signal from terminal a of signal generator 5 is now applied overback cont-act a of track relay 1TR to input terminals a of clamp 10,differentiator 15, negative limit detector 13, and positive limitdetector 14.

' Clamp 10 will now pass a signal to storage unit 18in accordance withthe output characteristics shown in FIG.

, 3. That is, if the signal generator output is below about 150 volts.However, if the output of signal generator 5' goes below 6 volts,negative limit detector 13 will clamp its output terminal b to 300 voltsminimum and prevent the discharge of capacitor C4. If the output of thesignal generator exceeds volts, positive limit detector 14 will operateto clamp its output terminal b to a minimum of 300 volts, which wouldalso prevent the discharge of capacitor C4.

Differentiator 15 will now proceed to measure the rate of change of thesignal from signal generator 5. The output at terminals b and c ofdifierenti-ator 15 is applied to input terminals a of negative limitdetector 16 and positive limit detector 17, respectively. Negative limitde-' tector 16 will function at avoltage more negative than 16 volts,and positive limit detector 17 will function at a voltage more positivethan +16 volts. These voltages correspond to a' permissible rate rangeof or .4 pound per ton per second. Should the rate of change exceedthese limits, one or the other of the limit detectors will clamp itsoutput terminal to a minimum of 300 volts and prevent the discharge ofcapacitor C4 in time delay unit 19.

At the end of three seconds, capacitor C1 in time delay unit 9 will havedischarged sufiiciently so that output terminal b of time delay unit 9will be clamped to a minimum of volts. If none of the limit detectorshave been actuated, capacitor C4 in time delay unit 19 can now begin todischarge from 300 volts to 150 volts. When this occurs, afteraproximately .7 second, the grid of triode V10 will be biased to 6l.5volts, causing triode V10 to cut off and triode V11 to conduct. Relay VRwill now pick up. If it happens that one of the limit detectors has beenactuated, such that capacitor C4 cannot discharge after time delay unit9 has functioned, this discharge can still take place at any time afterall of the limit detectors have been restored to normal and before tracksection 2T is occupied by the cut. Thus, relay VR will be operated .7second after the expiration of the initial time delay plus anyadditional time it takes to restore all of the detectors to normal. Ifthis occurs before track relay ZTR is released, relay H will be pickedup over front contact a of relay VR and front contact a of track relayZTR. The final value passed by clamp 10 will then be stored in storageunit 18.

While I have described one embodiment of my invention in detail, it willbe apparent that many changes and modifications could be made withoutdeparting from the scope of my invention. Accordingly, I do not wish tobe limited to the details shown, but only by the scope of the followingclaims.

Having thus described my invention, what I claim is:

1. In combination, measuring means for generating a signal in accordancewith the rolling resistance of a railway car, checking means controlledby said measuring means and actuated to a first or a second conditionaccording as said signal is within or exceeds a predetermined range, andstorage means controlled by said checking means in its first conditionfor storing said signal.

2. A validity detector, comprising, in combination, a ditferentiator,means for applying a signal to be evaluated to said ditferentiator,limit detecting means controlled by said difierentiator and actuated toa first or a second condition according as the rate of change of saidsignal is within or without prescribed limits, storage means, and meanscontrolled by said limit detecting means in its first condition foractuating said storage means to store said signal.

3. Apparatus of the class described, comprising, in combination,measuring means for generating a first signal in accordance with therolling resistance of a railway car, first limit detecting meanscontrolled by said measuring means and actuated to a first or a secondcondition according as said first signal is within or without apredetermined range, differentiating means controlled by said measuringmeans for producing a second signal in accordance with the rate ofchange of said first signal, second limit detecting means controlled :bysaid diiferentiating means and actuated to a first or a second conditionaccording as said second signal is within or without a predeterminedrange, and storage means controlled by said limit detecting means intheir first conditions for storing said first signal.

4. In combination, limit detecting means energized to a first conditionin response to an applied signal having a value within a predeterminedrange and energized to a second condition in response to an appliedsignal having any value not in said predetermined range, means forapplying a signal to said limit detectingmeans, a utilization device,and means controlled by said limit detecting means in its firstcondition for applying said signal to said utilization device.

5. Apparatus for checking the validity of a signal in accordance with aplurality of criteria, comprising, in combination, a diode for eachcriterion, means controlled by the signal to be checked for applying afirst voltage to each diode if its corresponding criterion is satisfiedand a second voltage to the diode if its corresponding criterion isunsatisfied, a capacitor, a plurality of parallel charging circuits forsaid capacitor, each circuit including one of said diodes, switchingmeans having a first condition and a second condition, means controlledby said capacitor for actuating said switching means to its first or itssecond condition according as said capacitor is charged to said first orsaid second voltage, and a circuit closed by said switching means in itsfirst condition to indicate the validity of said signal.

6. Means for evaluating the stability of a variable, comprising, incombination, a resistor, a capacitor, means for applying a voltage inaccordance with the value of the variable across said resistor andcapacitor in series, an amplifier controlled by the voltage across saidresistor, a high-pass degenerative feed-back path for said amplifier forfiltering noise, first and second Zener diodes connected in opposedrelation across said resistor for limiting the 0 voltage thereacross,and a limit detector controlled by sald 5 amplifier and actuated from afirst condition to a second conditon [by an amplifier output voltagebeyond a predetermined range.

7. A validity detector for a system comprising means for measuring avariable and storing a signal in accordance with the measured valuethereof, said detector comprising, means for delaying the storage ofsaid signal for a predetermined time after the beginning of ameasurement, means *for detecting excursions of the signal beyond apredetermined range, means for detecting instability in the signalbeyond predetermined limits, and means controlled by said detectingmeans for preventing the storage of the signal if it is excessive orunstable.

8. A validity detector, comprising, in combination, a relay, anamplifier connected to operate said relay, a capacitor, means forapplying a voltage developed across said capacitor to control saidamplifier, a plurality of parallel charging circuits for said capacitor,each charging circuit including a diode, means for biasing each of saiddiodes with a first voltage or a second voltage according as apredetermined characteristic of a signal is within or Without apredetermined range, control means for each biasing means, each biasingmeans responding to an applied signal to measure a differentcharacteristic of the signal, and means for applying a signal to saidcontrol means, said amplifier being adjusted to actuate said relay whensaid capacitor is charged to said first voltage and to release saidrelay when said capacitor is charged to said second voltage, wherebysaid relay is energized when and only when all said characteristics arewithin their prescribed ranges.

References Cited bythe Examiner UNITED STATES PATENTS 2,721,258 10/1955Freehafer 246-182 2,778,947 1/ 1957 Scherbatskoy.

2,817,076 12/ 1957 Graves 340248 2,839,681 6/1958 Schatz et al. 328-1272,846,522 8/1958 Brown 328-127 2,891,144 6/1959 Yalich et al. 246-1822,901,609 8/1959 Campbell 328-l27 2,907,022 9/ 1959 Kendall.

2,915,623 12/1959 Hughson 246182 2,928,002 3/1960 I-Iavstad.

2,965,889 12/1960 Cook et al. 34024S 2,971,084 2/1961 Meshelen-ich246-182 3,018,442 1/1962 Goodman.

3,045,183 7/1962 Laczko.

3,098,936 7/1963 Isabeau.

STEPHEN W. CAPEIJLI, Primary Examiner. SAMUEL BERNSTEIN, Examiner. L. T.HIX, Assistant Examiner.

1. IN COMBINATION, MEASURING MEANS FOR GENERATING A SIGNAL IN ACCORDANCEWITH THE ROLLING RESISTANCE OF A RAILWAY CAR, CHECKING MEANS CONTROLLEDBY SAID MEASURING MEANS AND ACTUATED TO A FIRST OR A SECOND CONDITIONACCORDING AS SAID SIGNAL IS WITHIN OR EXCEEDS A PREDETERMINED RANGE, ANDSTORAGE MEANS CONTROLLED BY SAID CHECKING MEANS IN ITS FIRST CONDITIONFOR STORING SAID SIGNAL.